Electrically driven rotary shear



1947. E. s. MURRAH 2.425,484

ELEGTRIGALLY DRIVEN ROTARY SHEAR Filed July 1.9, 19% I5 $heets--$heet 1INVENTOR. Emz mm .8. MURRAH A TT'OWA/EY Aug. 12, 1947. E. s. MURRAHBLECTRICALLY DRIVEN ROTARY SHEAR Filed July 19; 1946 i4 dl 3 Shams-Sheet2 (I? {LB (27 vv Tf 4 INVENTOR. EDMUND S. MURRAH 4" r ATTOR Y Aug. 12,1947. E. s. MURRAH 2,425,434

ELECTRICALLY DRIVEN noun swam Filed July 19, 1946 3 Shuts-Sheet 3 k bbINVENTOR. S. MURRAH BAR SPEED BAR SPEED c 6 5 h L L Q m c w Y DB w w w NE 0 0 0 m n n n. w U U m m m m O V O 0 kbw E f E E 5 2 fm fim R R m m mA 5 E H E H H 5 H 5 5 6 E E. L L c m Y C C 5 yet i i ca e we an2,i25,elil i E LE OTRMJAILLY DER/EN .ltQl'llAltlY SHEAR Edmund S.Mini-rah, Worcester, Mass, assignor to Morgan ilonsti'uction Company,Vlorcester, Mass, a corporation oi Massachusetts Application .July 19;19%, Serial No. 68%,856

- (6i. add-43$) llll (Claims. i

This invention. relates to electrically driven rotary shears, and moreparticularly to sc -called flying shears adapted to sever longitudinallymoving material into predetermined lengths.

For many years there has been a demand for an electrically driven rotaryshear capable of cutting metal billets into accurate lengths as theyissue at comparatively high speed from the final stand of the rollingmill, but the inherent diflicuL ties in this situation have heretoforeprevented a satisfactory solution. The principal diihculty arises fromthe necessity for matching the speed of the shear knives with the speedof the billet at the time of the cut, while allowing sufficient rangefor adjustment in the length of the severed pieces. Unless these speedsare properly synchronized, the cut will not be made in a proper mannerand the shear may be seriously damaged. Obviously, if a shear having saya nine foot shear circumference or knife circle operate at a uniformspeed in synchronisrn with the billet and makes a cut at everyrevolution, the severed lengths will be nine feet long. Also if such ashear is arranged for rnis-cuts so that it cuts every two revolutions orevery three revolutions, the severed lengths will be eighteen ortwenty-seven feet long respectively. In other words, it is relativelysimple to cut lengths which are equal to or multiples of the shearcircumference. Ordinarily however the billet must be out into lengthswhich; are not so directly related to the size of the shear, and ittherefore becomes necessary to provideacyclic variation in the speed ofthe shear, which presents a dlfilfiult problem because of the inertia ofthe moving parts. It has been proposed to effect this cyclic speedvariation by various mechanical means, for example by rocking adifferential gearing in the shear drive, but such constructions add tothe inertia problems and are very bulky and expensive. It has also beenproposed to vary the speed of the electric motor which drives the shear,in a cyclic manner, but no suitable and operative construction of thistype has been disclosed heretofore. l 'urtheidiificulties arise from thefact that the speed of the billet is usually subject to considerablevariation, and it therefore becomes necessary to maintain a propercutting speed for the shear knives and a uniform length for the severedpieces despite such variation in billet speed.

It is accordingly one object of the invention to provide an electricallydriven rotary shear which will cut rapidly moving stock into accuratelengths.

It is a :l'urther object or" the invention to provide an electricallydriven rotary shear capable of cutting metal billets as they emerge atrelatively high speeds from a rolling mill.

It is a further object of the invention to pro vide an electricallydriven rotary shear which may be readily adjusted to vary the length or"the severed pieces while maintaining proper synchronisrn of the speed ofthe shear with the speed of the stock; as each cut is made.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

Referring to the drawings illustrating one embodiment of the inventionand in which like reference numerals indicate like parts,

Fig. l is a somewhat diagrammatic plan view of a rotary shear and aportion of an associated billet mill;

Fig. 2 is a section taken on the line 2-2 of Fig. 1;

Fig. 3 is an electrical wiring diagram showing one means for driving theshear and controlling the speed thereof;

Fig. 4 is a fragmentary view showing a m0dification in the diagram ofFig. 3;

Fig. 5 is a graph showing certain relationships of the shear speed tothe shear revolutions, ob-

"tainable with the arrangement shown in Fig. 3;

Fig, 6 is a graph similar to Fig. 5, showing still furtherrelationships;

Fig. 'l is a graph showing certain relationships of the shear speed tothe shear revolutions, ob tainable with the arrangement shown in Fig.4', and

Fig. 8 is a graph similar to Fig. 7, showing still furtherrelationships.

Referring first to Figs. 1 and 2, there is provided a rotary shear idarranged to cut a hot metal billet B into predetermined lengths as itemerges from the finishing stand l l of a continuous billet mill andWhile a portion or the billet is still between the mill rolls l2. Theserolls are driven by an electric motor it which is connected to the rollsby the usual mill pinions (not shown) located within a pinion hOllSll'lgl5, and the usual universal spindles it. The motor i l also drives asmall pilot generator ll. A suitable roller table it? supports thebillet between the mill stand 1 i and the shear iii. A flag lid islocated in the path of the billet to control a normally open switch 2 l.

The rotary shear id may be of any suitable type, and for purposes ofillustration I have shown a shear constructed in accordance with thedisclosure of the patent to Morgan et al. No. 2,157,000, granted May 2,1939. This shear cornprises a pair of opposed horizontal crank shafts 23rotatably supported in a frame 24 and connected to one another by gears25. These gears are arranged to be driven by four electric motors 21which are connected to the gears by pinions 28. Each crank-shaft 23carries a knife head having a knife 3| thereon, and each knife head hasa rearwardly extending tail rod 32 with a roller 34 on its end, theroller being guided in a slot 35 in a stationary plate 36. At eachrevolution of the crank shafts, the knives 3|, will meet to sever thebillet as it travels longitudinally between them. For purposes ofcontrol, as will be explained hereinafter, a limit switch mechanism 3!is connected to the upper crank shaft 23 to be driven thereby.

Referring now to Fig. 3, it will be seen that ill) the fields 39 of theshear motors 21 are connected across a suitable source 48 of constantvoltage direct current, under the control of a main switch 4|. Thesemotors are provided with the usual mechanical brakes which may be heldin the released position by one or more solenoids 42. The armatures ofthe motors 21 are connected in a circuit with a direct current generator43, this circuit including a normally open switch 44 under control ofthe coil 45 of a magnetic contactor. This coil also controls a normallyopen switch 46 which is connected in series with the solenoid 42 acrossthe source 40. The generator 43 is driven by a motor 41 which isenergized from a source 48 of alternating current. The field 50 of thegenerator 43 is energized by a direct current generator 5| forming aregulating exciter, which is driven by a motor 52, this motor beingenergized from a source 53 of alternating current. The exciter 5| ispreferably of the well-known amplidyne type having, in addition to theusual anti-hunt field and load control fields (not shown), a controlfield 55 and a reference field 56. This provides a Ward Leonard oradjustable voltage control for the shear motors 21 so arranged that thespeed of these motors will be a function of the voltage supplied by thegenerator 43, this voltage in turn being under the control of theregulating exciter 5|. The reference field 56 is more powerful than thecontrol field 55, and these two fields oppose one another.

In order to control the voltage which is sup plied by the exciter 5i tothe generator field 50, certain control apparatus is provided and willnow be described. Thus the pilot generator H (which is driven by themill motor l4 of Fig. 1) has two opposed fields 58 and 59. The field 58is connected in circuit with one winding of a transformer 60, the otherwinding of the transformer being connected across the terminals of thegenerator 43. There are also shown four resistances 62, 63, 64 and 65,and a rectifier 66. A magnetic contactor is provided having a coil 68controlling two normally open switches 69 and 10, and a normally closedswitch H. A further magnetic contactor is provided having a coil 13controlling six normally open switches l5, 16, ll, l8, l9 and 80. Afurther magnetic contactor is provided having a coil 82 controlling anormally closed switch 83 and two normally open switches 84 and 85. Astill further magnetic contactor is provided having a coil 81controlling a normally closed switch 88 and two normally open switches89 and 90. The limit switch mechanism 3'! includes three switches 92,93, and 94 which are controlled by three rotatable cams 95, 96 and 9lrespectively arranged to rotate once for each cycle or cut oi the shearl0. Thus ii the shear makes a cut at each revolution, as in theparticular case illustrated, the cams will rotate at the same speed asthe shear. If the shear is arranged to make niis-cuts and to cut sayevery two revolutions or every three revolutions, the cams should rotateat one-half or one third the speed of the shear, respectively.

The electrical connections for the various switches and other deviceswill now be described. The resistance 63 is connected in series acrossthe terminals of the generator 43. The rectifier 66, the switch 15, theexciter control field 55, and the armature of the pilot generator I! areconnected in a series circuit which in turn is connected across aportion of the resistance 63, The resistance 62 is connected across theswitch 15. The switch 16 and the reference field 56 of the exciter 5|are connected in series across the source 40. The resistance 64,the'switch 89, and the field 59 of the pilot generator are connected inseries across the source 40. This resistance 64 is provided with aslider I to form an adjustable rheostat, and the switch 69 is connectedacross a portion 01 the resistance by means of this slider. Theresistance 65, the switch 88, and the field 59 of the pilot generatorare connected in series across the source 49. The flag switch 2| and thecoil 68 are connected in series across the source 40. The switch 10 andthe coil 13 are connected in series across the source 45. The switch H,the switch 83, and the coil 13 are connected in series across the source40. The switch 93 is connected in parallel with the switch 83. Theswitch 18 is connected in series with the coil 45 across the source 40.The switch 92 is connected in series with the coil 82 across the source40. The switches H, 19, and 84, and the coil 82 are connected in seriesacross the source 40. The switches 80 and 85, and the coil 81 areconnected in series across the source 40. The switches 9|] and 94 areconnected in a series circuit which in turn is connected across theswitch 85.

It will now be apparent that in the operation of this embodiment of theinvention, the switch 4| will be closed, and the generator 43 and theexciter 5| will be driven at substantially constant speeds by theirrespective motors 4! and 52. The pilot generator l1 will be driven at aspeed Which bears a definite ratio to the speed of the mill rolls l2 andof the billets B issuing therefrom. As the front end of a billetapproaches the flag 2!]. the switch 44 will be in its open position, andthe shear motors 21 will be stationary. The shear l0 will be stationary,with the crank shafts 23 approximately degrees from the cuttingposition, and the earns 95, 96 and 9'! positioned as shown in Fig. 3. Asthe front end of the bar engages the fiag 20, it will close the switch2| and energize the coil 68 closing the switches 69 and 10, and openingthe switch H. the coil 13 will be energized, thus closing the switches15, 1 6, ll, l8, l9 and 80. As the switches '15 and 16 close, theexciter fields 55 and 56 will be energized, so that the excitcr 5| willenergize the field 50 of the generator 43. The closed switch 11 willprovide a holding circuit for the coil 13. As the switch 18 closes, thecoil 45 will be energized. thus closing the switches 42 and 44 andstarting the shear motors 21, which will accelerate and bring the speedof the shear knives 3| into syn- ChlOnlSIl'l with the speed of thebillet before the As the switch 10 closes,

knives have reached the cutting position. In the meantime, the frontportion of the billet B will have reached a position between the knives,and as the knives come together they will cut a short crop from thefront end of the billet.

The shear speed is held equal to the billet speed, during each cut, bythe action of the regulating exciter 5| in conjunction with the pilotgenerator H. The excitation of the pilot generator field 59 is constant,and determined by the value of the resistance 65. The excitation of thereference field 5B is also constant, whereas that of the control field55 varies with the speed of the pilot generator H and with the voltageoutput of the shear generator 43. Since the two fields 55 and 56 opposeone another, the latter being the greater, the voltage or output of theregulating exciter 5| is a function of the difference between theexcitations ofthese fields. The voltage produced by the pilot generatorI! and the voltage produced by the shear generator 43 act in oppositionto one another incontrolling the excitation of the control field 55, andthe regulating exciter 5! will vary the excitation of the sheargenerator 43 to 'maintain a balanced condition such that the shear speedis equal to the billet speed. Thus, if the billet speed should increaseever so little, the pilot generator l1 would provide a greater voltage,in opposition to the shear generator voltage, thus decreasing theexcitation of the control field 55, and causing the regulating exciterto increase the excitation of the field 59, which will increase thevoltage produced by the shear generator 43 and increase the speed of theshear motors 21. As the shear reaches billet speed, the voltage producedby the generator 43 will have increased just enough to establish abalanced condition. The function of the rectifier 66 is to block theflow of electricity in one direction, and. thereby prevent the controlfield 55 from being reversed, as might otherwise occur under certainconditions, The purpose of the resistance 62 is to permit a limited flowof current through the control field 55 even with the switch open. Thetransformer 80 operates only during periods of shear motor accelerationor deceleration, when the voltage applied to the transformer by theshear generator 43 is changing. At such times a current will be inducedby the transformer to excite the pilot generator field 58 in such adirection as to oppose the rate of shear motor acceleration ordeceleration, as the case may be and thereby prevent the control fromover shooting. At other times, the field 58 Will remain unexcited.

At the completion of the cut, and preferably immediately after the shearknives have cleared the billet, the cam 95 will close the limit switch92 momentarily, thereby energizing the coil 82,

thus opening the switch 83 and closing the switches 84 and 85. At thesame time, cam 91 will close the limit switch 94. Closing the switch 85will energize the coil 87, thus opening the switch 88 and closing theswitches 89 and 90, the latter completing a holding circuit for the coil81. As the switch 88 opens and the switch 89 closes, the energization ofthe pilot generator held 59 will be placed under the control of therheostat 64 rather than the resistance 65, and the shear motors 21 willdecelerate or accelerate as the case may be) to an idling speed whichmay be either less than or greater than the cutting speed, dependingupon the particula lengths which are to be cut from the billet. Thus ifthe severed lengths required are longer than the circumference of theshear circle, i. e., the orbit of the centers of the shear cranks, theidling speed must be less than the cutting speed. If the requiredlengths are less than the shear circle circumference, the idling speedmust be greater than the cutting speed. The idling speed, andconsequently the lengths of the severed pieces, may be controlled byadjusting the slider I00.

After the shear has operated at its idling speed for a time, and as theknives again approach. the billet, the cam 91 will open the limit switch94 and de-energize the coil 8?, thereby closing the switch 88, andopening the switches 89 and 90. This will again place the excitation ofthe pilot generator field 59 under the control of the resistance 65, andas a result the shear motors will promptly accelerate or decelerate (asthe case may be) to synchronous cutting speed. This speed will beattained before the knives engage the billet, and the cut willaccordingly be made in a proper manner.

Fig. 5 shows therelationship of the shear speed to the shear revolutionswhen cutting lengths which require a slowing down of the shear betweencuts. As indicated, the shear will travel at bar speed during each cut,and as soon as the knives have cleared \the' bar the shear will slowdown to an idling speed which is determined by the setting of therheostat64. At a predetermined point in the revolution of the shear, it

'will start to accelerate to bar speed in time for Fig. 6 shows therelationship of the shear speed to the shear revolutions when cuttinglengths which require a speeding up of the shear between cuts. In thiscase the shearrwill travel at bar speed during each cut, and as soon asthe knives have cleared the bar the shear will accelerate to an idlingspeed which is determined by the When the shear.

setting of the, rheostat 64. reaches a predetermined position it willstart to decelerate to bar speed in time for the next cut. The fulllines, the dotted lines, and the dot-anddash lines indicate variousidling speeds which may be employed to produce various lengths ofsevered pieces.

As the tail end of the bar leaves the flag 29, the switch 2| will open,de-energizing the coil 68, opening the switches 69 and I0, and closingthe switch H. Opening the switch 69 will increase the eifectiveresistance of the rheostat 84 and thereby reduce the idling speedof theshear. The coil 13 will remain energized through the switches 11' and93, despite the opening Of the switch 10. As the cam 95 closes theswitch 92, and the cam 91 closes the switch 94, the coil 82 will beenergized, opening the switch 83, and closing the switches 84 and 85.Closing the switch 85 will energize the coil 81, which will open theswitch 88, and close the switches 89 and 90. Closing the switch 89 willplace the shear under the control of the resistance 64, which hasalready been increased an effective amount by the opening of the switch68, and the shear will imme diately decelerate to a very low idlingspeed. The cam will open the switch 92 shortly after it was closed, butthe coil 82 will remain energized through the closed switches l I, 19and 84. As the shear cranks reach the position shown in the drawings,the cam 96 will open the switch 93 and thereby de-energize the coil 13,opening the i and B5.

accuses 7 switches l5, 16, "ll, "l8, "l9 and ill]. switch 19 willdeenergire the coil 82, theie...- ,r clos ing the switches 83 andopening the switches B4 Opening the switch 80 will de-cnergize the coil81, thereby closing the switch 88 and opening the switches 89 and 90.Opening the switch (B will (lo-energize the coil 45 and open theswitches 42 and 44, thus disconnecting the shear motors 21 from thegenerator 43 and deenergizing the brake solenoid 42. The mechanicalbrakes will thereupon bring the shear to an immediate stop.

With the Ward Leonard system and amplidyne control, as described, veryrapid changes in shear motor speed are obtainable, and as a result theshear may be used for cutting billets at high speeds and it may bereadily adjusted to cover a wide range of severed lengths. Duringdeceleration of the shear motors, which occurs once for each cut, thespeed reduction is effected by means of regenerative braking. In otherwords, when the voltage produced by the generator 43 is re duced, theshear will drive the motors 21, which will serve as generators, and theyin turn will drive the generator 43, which will serve as a motor todrive the motor 41, the latter operating under these conditions as agenerator to return electrical energy to the source 43. Suchregenerative braking very effective in producing extremely rapiddeceleration, and it results in a considerable saving in powerconsumption.

It will be noted that in the embodiment illustrated in Fig. 3 the switch94, which initiates the speed change required to return the shear to barspeed in preparation for each cut, is controlled mechanically by the cam91. Thus the required speed change always begins at a definite point inthe rotation in the shear.

In Fig. 4 there is shown a slight modification in which the cam 91 isomitted, and the switch 94 is controlled by an electronic time delayrelay H having a rheostat III which permits adjustment of the timedelay. Operation of this relay is initiated by closure of a normallyopen switch l|2 controlled by the coil 81, the arrangement otherwisebeing the same as in Fig. 3.

In the operation of the modification shown in Fig. 4, the coil B! willbe energized by the action of the cam 95 (as previously described inconnection with the embodiment of Fig. 3) immediately after the kniveshave cleared the bar, thus closing the switches 89, 90 and H2, andopening the switch 88. This Will cause the shear motors to decelcrate(or accelerate, as the case may be) toward the idling speed determinedby the setting of the rheostat 64. Closing the switch H2 will place therelay H0 in operation, and after a predetermined delay (dependent uponthe setting of the rheostat l l I) this relay will time out and open theswitch 94, de energizing the coil 81. As in the Fig. 3 arrangement, thisWill cause the shear motors to accelerate (or deceleratc as the case maybe) to the cutting speed. Thus the opening of the switch 54, whichinitiates the speed change required to return the shear to bar speed inpreparation for each cut, will take place at a predetermined time afterthe knives have cleared the bar and the cam 55 has closed the switch 92.By adjusting this time, tl'iroueh the medium of the rheostat ill, thelength of the severed pieces may be controlled.

'7 illustrates diaerammatlcally the changes in sheer speed which takeplace when the Fig. 4 arrangement i used to cut lengths requiring aslowing down of the shear between cuts. As

ljlrlening; the

indicated by the full lines, the dotted lines, and the dot-and-dashlines, the shear will revolve at bar speed during eachcut, decelerate assoon as the knives clear the bar, and accelerate to bar speed at varyingtimes dependent upon the adjustment 0f the time delay relay H0. If thelengths to be out are only slightly longer than the circumference of theshear circle, the acceleration may begin before the shear has reachedits idling speed.

Fig. 8 similarly shows the speed changes which take place when thelengths to-be out are such as to require a speeding up of the shearbetween cuts. The lines indicate that the shear will accelerate promptlyas the knives clear the bar, and decelerate to the bar speed before thenext cut is made, the deceleration starting at varying times dependentupon the adjustment of the time delay relay III). In the case of lengthswhich are only slightly shorter than the shear circle circumference, thedeceleration will start before the shear has reached its idling speed.

It will now be apparent that the invention provides an electricallydriven rotary shear which is capable of cutting very rapidly movingstock into accurate lengths. In particular the invention makes itpossible to cut metal billets as they emerge from a rolling mill andwhile a portion of the billet is still passing through the rolling mill.The arrangement is such that the cuts will be made accurately and in aproper manner despite variations in the delivery speed of the mill.

Having thus described my invention what I claim a new and desire tosecure by Letters Patent is:

1. Shearing apparatus comprising a rotary flying shear for cuttinglongitudinally traveling material, means for feeding material to theshear, an electric motor connected to the shear to drive the same, meansto accelerate the motor and to decelerate the motor once for eachcutting cycle of the shear, and means effective during such decelerationto cause the motor to operate as an electric generator.

2. Shearing apparatus comprising a rotary flying shear for cuttinglongitudinally traveling material, means for feeding material to theshear, an electric motor connected to the shear to drive the same, meansestablishing a cutting speed for the motor corresponding to the speed ofthe material, means establishing an idling speed for the motor differentfrom the cutting speed, means to change the motor speed from cuttingspeed to idling speed and vice versa once for each cutting cycle of theshear, one of the speed changes being a deceleration, and meanseffective during such deceleration to cause the motor to operate as anelectric generator.

3. Shearing apparatus comprising a rotary flying shear for cuttinglongitudinally traveling material, means for feeding material to theshear, an electric motor connected to the shear to drive the same, meanestablishing a cutting speed for the motor corresponding to the speed ofthe ma terial, means establishing an idling speed for the motorcliiierent from the cutting speed, means operating in timed relationwith the shear and effective shortly after completion of each. cut tochange the motor speed from cutting sp ed to idling speed, meanseffective before the next cut to change the motor speed to cuttingspeed, one of the speed changes being a deceleration, and meanseffective during such deceleration to cause the motor to operate anelectric generator.

4. Shearing apparatus comprising a rotary flying shear for cuttinglongitudinally traveling material, means for feeding material to theshear, an electric motor connected to the shear to drive the same, amain electric generator connected in circuit with the motor and having afield, means to excite the generator field, and means to change theexcitation of the generator field and thereby change the speed of themotor twice during each cutting cycle of the shear, one of the changesin excitation causing the generator voltage to be reduced so that themotor will operate as an electric generator and decelerate at a rapidrate.

5. Shearing apparatus comprising a rotary fiying shear for cuttinglongitudinally traveling material, means for feeding material to theshear, an electric motor connected to the shear to drive the same, amain electric generator connected in circuit with the motor and having afield, a regulating exciter connected incircuit with the genmeans toexcite thecontrol field, and means to increase and decrease theexcitation of the control field once during each cutting cycle of theshear and in timed relation to the rotation thereof, thereby producing acyclic variation in the speed of the shear.

6. Shearing apparatus comprising a rotary fiying shear for cuttinglongitudinally traveling material, means for feeding material to theshear, an electric motor connected to the shear to drive the same, amain electric generator connected in circuit with the motor and having afield, a regulating exciter connected in circuit with the generatorfield, the exciter having a reference field and a control field, meansproviding a constant 35 excitation for the reference field, means toexcite the control field, and means to increase and decrease theexcitation of the control field once during each cutting cycle of theshear and in timed relation to the rotation thereof, thereby 40producing a cyclic variation in the speed of the shear.

'7. Shearing apparatus comprisingamtary'fiyulating exciter connected incircuit with the generator field, the exciter having a control field.

a pilot generator having a field, means subjecting 1 the control fieldto a voltage which is a,,function of the voltage produced by the maingenerator and of the voltage produced by the pilot generator, means todrive the pilot generator at a speed bearing a definite ratio to thespeed of the material, means to excite the pilot generator field, andmeans to increase and decrease the excitation of the pilot generatorfield once during each cuttingcycle of the shear and in timed relationto the rotation thereof, thereby producing acyclic variation in thespeed of the shear.

9. Shearing apparatus comprising a rotary fiying shear for cuttinglongitudinally traveling metal bars, a rolling mill arranged todeliverbars to the shear and to control the speed of the bars, anelectric -motor connected to the ferator field, the exciter having acontrol field, 2o shear to drive the same, a main electric gen-- eratorconnected in circuit with the motor and having a field, a regulatingexciter connectedtincircuit with the generator field, the exciter havinga control field, a pilot'generator having a; field, means subjecting thecontrol field to a voltage which is a function of the voltage producedby the main generator and of, the voltage pro- 10. Shearing apparatuscomprising a rotary fiying shear for cutting longitudinally travelingmetal bars, a rolling mill arranged to deliver bars to the shear and tocontrol the speed of the bars, an electric motor connected to the shearto drive the same, a main electric generator con- "nected in circuitwith the motor and having a:

ing shear for cutting longitudinally traveling "ma terial, means forfeeding material to the shear, an electric motor connected to the shearto drive the same, a main electric generator connected in circuit withthe motor and having a field, a regulating exciter connected in circuitwith the generator field, the exciter having a control field, a pilotgenerator connected in circuit with the control field, the pilotgenerator having a field, means to drive the pilot generator at a speedbearing a definite ratio to the speed of the material, means to excitethe pilot generator field, and means to increase and decrease theexcitation of the pilot generator field once during each cutting cycleof the shear and in timed relation to the rotation thereof, therebyproducing a cyclic ffield, a regulating exciter connected in circuitwith the generator field, the exciter having a control field, a pilotgenerator having arfield, means subjecting the control field to avoltage which is a function of the voltage produced by the maingenerator and of the voltage produced by the pilot generator, means todrive the pilot generator at a speed bearing a definite ratio to thespeed of the rolling mill, means providing two excitation circuits forthe pilot generator field, the first of the excitation circuits beingsuch as to establish a cutting speed for the shear in synchronism withthe speed of the bars and the second excitation circuit being such as toestablish an idling speed for the shear different from the cuttingspeed, and means operable in timed relation with the rotation of theshear to render the first excitation circuit effective during each 'cutand to render the second excitation circuit efiective for a portion ofthe cycle between successive cuts.

EDMUND S. MURRAH.

